The present invention relates to a cathode ray tube used in a color television receiver or a terminal display of a computer, and more particularly to a plate-type cathode ray tube device.
For example, a first one of conventional plate-type cathode ray tube devices is disclosed in a Japanese Patent Publication JP-A-46-2619, and a second conventional plate-type cathode ray tube device is disclosed in a Japanese Patent Publication JP-A-60-189,849.
The structure of the first conventional device will be explained below, with reference to FIG. 16. Referring to FIG. 16, a fluorescent screen 2 is formed on the inner surface of a face plate 1 of a vacuum vessel (not shown), and a plurality of deflection electrodes 41 each extended in a horizontal direction are formed on a back panel 3 which is provided in parallel to the fluorescent screen 2. In more detail, the deflection electrodes 41 are juxtaposed at regular intervals in a vertical direction. Further, a plurality of electron guns are provided at the bottom of a spatial region sandwiched between the fluorescent screen 2 and the deflection electrodes 41, in such a manner that the electron guns are arranged at regular intervals in a horizontal direction. The electron guns are made up of an electron source 71 and two control electrode plates 82 and 83. That is, thermal electrons emitted from the electron source 71 pass through apertures which are provided in each of the control electrode plates 82 and 83, to form a plurality of electron beams 10 which are intensity-modulated independently of each other. Further, the first to n-th deflection electrodes 41 viewed from the electron gun side are applied with a voltage equal to a voltage applied to the fluorescent screen 2, and the (n+1)th and following deflection electrodes 41 are applied with a voltage lower than the voltage applied to the fluorescent screen 2. Thus, the electron beams 10 emitted from the electron guns run straight till the electron beams reach the vicinity of the n-th deflection electrode 41, and are then deflected toward the fluorescent screen 2 by a repulsive force from the (n+1)th and following deflection electrodes 41. As a result, those portions of the fluorescent screen 2 which are bombarded with the electron beams 10 emit light in accordance with the modulated intensities of the electron beams, and thus a scanning line is formed on the screen 2. By sequentially changing the n-th deflection electrode 41 by changing the numerical value n, the fluorescent screen 2 can be scanned with each electron beam 10 in a vertical direction because the n-th deflection electrode 41 is applied with the same voltage as the voltage which is applied to the fluorescent screen 2 from an external power supply.
In the second conventional device, as shown in FIG. 17, a single vertical deflection electrode 42 (that is, a single plane electrode) is formed on the back panel 3, in place of plural deflection electrodes 41 of FIG. 16. Further, a plurality of plane electrodes 52, 53, 54, each having an aperture 55 which is extended in a vertical direction and corresponds to one of a plurality of electron beams 10, and a plurality of horizontal deflection electrodes 62, each extended in a vertical direction, are disposed between the vertical deflection electrode 42 and the fluorescent screen 2. In more detail, a pair of horizontal deflection electrodes 62 are provided for each of the electron beams 10, to deflect the electron beam in a horizontal direction. Further, an auxiliary deflector 87 is provided between the electron guns and the vertical deflection electrode 42. Thus, the electron beam emitted from an electron gun is deflected by the auxiliary deflector 87 in a direction perpendicular to the fluorescent screen 2, and is then deflected toward the fluorescent screen 2 by a repulsive force from the vertical deflection electrode 42. Thus, in a case where the electron beam is deflected by the auxiliary deflector 87 so as to go near the vertical deflection electrode 42, the electron beam impinges on the fluorescent screen 2 at a position far from the electron gun. While, in a case where the electron beam is deflected by the auxiliary deflector 87 so as to go away from the vertical deflection electrode 42, the electron beam impinges on the fluorescent screen 2 at a position near the electron gun. Hence, the fluorescent screen 2 can be scanned with the electron beam 10 in a vertical direction, by controlling the deflecting direction given by the auxiliary deflector 87. Each of the electron beams 10 deflected toward the fluorescent screen 2 is subjected to the focusing action in a horizontal direction by one of the plane electrodes 52, 53, 54 and then deflected in a horizontal direction by a pair of horizontal deflection electrodes 62, to impinge on the fluorescent screen 2. Thus, the electron beams 10 form a plurality of electron beam spots on the fluorescent screen 2. When each electron beam 10 is deflected in a horizontal direction by an amount corresponding to the distance between adjacent electron guns, one scanning line can be formed on the fluorescent screen 2 by bright lines each scanned with one electron beam.
In the first and second conventional devices, there arises a problem that it is impossible to make the shape of electron beam spot constant all over the fluorescent screen. Further, the first conventional device is not provided with horizontal scanning means, and hence cannot obtain a satisfactory resolution in a horizontal direction. In order to improve the resolution in a horizontal direction, it is necessary to increase the number of electron beams, and thus the device becomes large in scale. In order to perform a vertical scanning operation, the first conventional device is required to include deflection electrodes, the number of which is not less than the number of scanning lines. Hence, it is very difficult to control many electron beams uniformly. Further, in order to drive many deflection electrodes with low power consumption, the first conventional device is required to have a complicated construction. In the first conventional device, the electron beam is subjected to the focusing action in a horizontal direction only by the electron gun, and thus it is impossible to keep the shape of electron beam spot optimum all over the fluorescent screen.
In the second conventional device, the influence of the vertical deflection electrode on an electron beam varies greatly with the deflecting direction given by the auxiliary deflector. As a result, the focused state of the electron beam at the top of the fluorescent screen is greatly different from that of the electron beam at the bottom of the fluorescent screen. Unlike the first conventional device, the second conventional device is provided with horizontal scanning means, and hence can obtain a satisfactory horizontal resolution by using a relatively small number of electron beams. However, the second conventional device is provided with a plurality of plane electrodes each for the focusing action in a horizontal direction, in addition to the horizontal deflection electrodes, and hence is obliged to become complicated in structure and large in scale.